Method of making shaped carbonaceous bodies

ABSTRACT

Shaped graphitic or graphite-like carbonaceous bodies are produced by forming binder-coated particles of a carbonaceous filler in a slurry, shaping the slurry or paste of the particles to the desired configuration, drying and cokefying the shaped body. The system is suitable for the production of graphitic structures for use in high-temperature gas-cooled nuclear reactors, as casting molds and the like. The present invention starts with the assumption that binder-coated filler particles are available, the particles having been coated uniformly (e.g. as described in our application Ser. No. 267,480).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.267,479 filed June 29, 1972, now U.S. Pat. No. 3,927,187.

This aplication is also related to application Ser. No. 267,480 filedJune 29, 1972, now U.S. Pat. No. 4,009,143.

FIELD OF THE INVENTION

Our present invention relates to a method of producing without pressureshaped carbonaceous bodies and, more particularly, to the productionwithout pressure of graphitic or graphite-like bodies(synthetic-graphite bodies) having good mechanical properties atrelatively low cost, said bodies consisting of binder-coated fillerparticles.

BACKGROUND OF THE INVENTION

In the art of forming carbonaceous bodies, it is frequently desirable touse carbonaceous materials which may be waste products or byproducts ofother processes as a source of graphitic carbon although thecarbonaceous material may be in an amorphous or nongraphitic state. Forexample, petroleum coke, carbon black and even electro graphite ornatural graphite are desirable sources of graphitic material for theproduction of shaped graphite or graphite-like bodies.

Graphite bodies have been employed heretofore for many purposes and invarious industries. For example, high-temperature gas-cooled nuclearreactors may make use of graphitic bodies for the structure of thenuclear-reactor core, as sheaths for nuclear-fuel elements, asenclosures for fertile elements in breeder reactions, and as componentsof nuclear fuel or breeder particles. In the metallurgical industry andin the glass-making field, graphite molds or molds lined with graphiteor graphite-like materials are used for casting. In general, graphiticbodies have been employed whenever high-temperature processes may beinvolved because they have a refractory and generally inert character.In nuclear reactors especially, they have proved to be desirable becauseof the neutron cross-section of graphitic materials and their reducedtendency to produce reaction products which interfere with the operationof a nuclear reactor.

Common methods of producing graphite-like bodies involve the extrusionof ram-pressing of synthetic graphite or graphite-like products to shapethem into the desired configuration. These systems frequently requireafter-treatment of the graphite-like bodies and make use of relativelyexpensive equipment because it has been difficult heretofore to impart awell-defined shape to the graphitic materials and at the same timeprovide high compressive strength and other desirable mechanicalproperties.

OBJECTS OF THE INVENTION

It is, therefore, the principal object of the present invention toprovide a method of making shaped bodies of synthetic graphite ormaterials similar to synthetic graphite, i.e., to produce graphite-likebodies, whereby the disadvantages of earlier systems can be avoided andwithout using pressure relatively intricate bodies can be made with goodmechanical characteristics at relatively low cost.

It is another object of the invention to provide an improved method ofmaking graphite-like bodies of uniform or homogeneous cross-section,highly compressive strength and complex configuration without thedisadvantages of ram-press systems as described above.

Yet another object of the invention is to provide a method of makingshaped carbonaceous, especially graphite-like bodies for use in nuclearreactors and as casting molds, without the use of pressure and with highstructural strength.

It is also an object to advance the principles set forth in theabove-mentioned applications.

SUMMARY OF THE INVENTION

These objects and others which will become apparent hereinafter areattained, in accordance with the present invention, in a system forproducing graphite-like bodies (synthetic-graphite bodies) whichcomprises the steps of forming a viscous slurry of particles in a liquidmedium, e.g. as a flowable or kneadable mass, shaping this mass to thedesired configuration, drying the mass and thereafter cokefying themass, the solids of which consist of particles of a carbonaceous fillercoated with a carbonizable binder. The present invention starts with theassumption that binder-coated filler particles are available, theparticles having been coated uniformly (e.g. as described in ourapplication Ser. No. 267,480 now U.S. Pat. No. 4,009,143).

According to a feature of the invention, the proportion of the liquid(solvent) in which the binder is soluble and which is miscible with theslurrying liquid, should be between 5 and 20% by volume of the liquidmixture.

During drying, the mass, which is preferably shaped in a mold, producesa solid "green" body which, upon cokefying at temperatures of 800° C andabove, yields a homogeneous rigid structure of the configurationoriginally imparted to the shapable mass. The latter can be employed asa more or less flowable or viscous product which may be sufficientlyfluid to be cast or may be somewhat more pasty so as to be shapable bymanipulative molding or kneading as in the case of clay.

According to another feature of the invention, the mass includes aliquid phase in which the binder is only limitably soluble andswellable, the liquid phase, e.g. water, serves as a vehicle for shapingthe particulate mass. Advantageously, the powder is obtained by dryingthe slurry of a binder and the aforementioned filler solids as describedabove.

Still another feature of the invention resides in the treatment of thepowder after it has been shaped, e.g. in the mold, with vapor of aboiling liquid comprising a solvent in which the binder is completely orpartially soluble, whereupon the shaped body is dried and cokefied inthe manner described. The powder is, in this case as well, produced bydrying the binder/solids slurry mentioned earlier. The body may have anespecially high density if the powder, before treatment with vapor isdensified by vibration in the mold. The vapor should consist 10 to 80%by volume of vapor of the binder-solublizing solvent. Best results areobtained when the binder-solublizing solvent in the vapor is present inan amount of 25%.

Preferably the filler materials, such as electrically-produced syntheticgraphite, natural graphite, milled petroleum coke and carbon black aremixed with binders such as pitch, tar and phenol-formaldehyde resins bydissolving the binder first in a liquid in which the filler is slurriedand then introducing this produced slurry into a carrier liquid in whichthe binder is insoluble or only partly soluble to produce an emulsion ofthe binder in the form of the coating upon the solid particles whichsettle and, after decanting of the excess liquid, form a slurry asdescribed in the commonly assigned copending application Ser. No.267,480 filed June 29, 1972 (now U.S. Pat. No. 4,009,143) in which weare coinventors, to produce particles in which the solid grains aresubstantially uniformly coated with the binder, the starting point ofthe present invention.

The shaped bodies produced in accordance with the present invention havean exceptionally high degree of homogeneity.

Another advantage of the process according to the present invention isthat nearly the whole porosity of the finished body is open and thus thebody is suitable as an impregnatable structure for any purpose in whichimpregnation is desired. For example, it may be desirable to impregnatethe body with conductive substances in order to increase the electricalconductivity, synthetic graphite bodies prepared with binders beingnotoriously of poor conductivity.

It is important to note, in accordance with this invention, that thesystem obtains bodies of relatively high density and strength withoutthe application of any pressure other than the self-packing orgravitational pressure resulting when the slurry is filled into a mold.

We have now found that it is not necessary to press the particles intoshape in an extrusion press, with rams or the like in order to obtainbodies of high density and high structural strength. Rather, the presentinvention teaches that it is possible to provide shaped bodies from suchcoated particles in a simple and economical way when the coatedparticles are slurried and are introduced as a wet or moist mass, as aslurry, into forms or molds and only then dried. It is indeed surprisingthat the slurrying of the particles into the mold, without applicationof pressure, can give rise to bodies which upon cokefication, formbodies equal to those produced under elevated pressures.

According to a feature of the invention, the proportion of the liquid inwhich the binder is soluble and which is miscible with the slurryingliquid should be between 5 and 20% by volume of the liquid mixture.

DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in whichthe sole FIGURE is a flow diagram illustrating a process according tothe present invention.

SPECIFIC DESCRIPTION

In a slurry receptacle 52, which is selectively supplied with a slurrythrough a line 60 from a process corresponding to that described inapplication Ser. No. 267,480, (U.S. Pat. 4,009,143) or a slurry from avessel 50 via line 51 in which a dry bindercoated powder is mixed with aliquid containing a solvent in which the binder is partially soluble,the slurry is introduced into a porous-wall form 53.

Preferably the liquid phase of the slurry is water containing 5 to 20volume percent methanol. In the form 53, the slurry is settled by avibrator 54, the excess liquid draining through the walls or beingdecanted, the contents of the mold being then degassed by heating it toa temperature of 70° C.

As represented at 54' the liquid phase is removed and the mold or formcontaining the particles from which the liquid has been removed isintroduced into a drying and hardening oven 55 and then introduced intoa furnace 56 where coking occurs as described in CARBON AND GRAPHITEHANDBOOK, CHAS. L. MANTELL, INTERSCIENCE PUBLISHERS, NEW YORK 1968. Theproduct is removed from the mold and constitutes the desired graphiticbody.

SPECIFIC EXAMPLE

75 Grams of a dry powder produced by a method described in applicationSer. No. 267,480 (now U.S. Pat. No. 4,009,143) are made into a pastymass by the addition of 15 volume percent of methanol containing water.The paste is thoroughly blended and shaped in a mold having wallspermeable to gas without pressure and thereafter the mold is heated to70° C. In the mold the mass is setting up from the liquid phase and thebody in the mold is then dried at about 105° C and is then coked at atemperature above 800° C. Cokefication is completed when the volatilecomponents of heating of the phenol-formaldehyde resin are no longergiven off. (Cokefication was carried out as described in Carbon andGraphite Handbook, Charles L. Mantell, Interscience Publishers, NewYork, 1968). The body is found to have a homogeneous structure, highmechanical strength and faithful conformity to the mold.

We claim:
 1. A method of making a graphitic body from carbonaceousfiller particles selected from the group which consists of petroleumcoke, electrographite, natural graphite and carbon black, coated with abinder selected from the group which consists of phenol-formaldehyderesin, pitch and tar, comprising the steps of:a. forming a paste orslurry of the binder-coated filler particles in a carrier liquidcontaining 5% to 20% by volume of a solvent for said binder, said binderbeing at most slightly soluble in said liquid; b. introducing said pasteor slurry into a mold wherein said paste or slurry is shaped without theapplication of pressure; c. drying the paste in said mold to form ashaped body therein; and d. cokefying said body.
 2. The method definedin claim 1 wherein said binder is a phenol-formaldehyde resin, saidsolvent is methanol and said liquid is water, said paste or slurry beingdried at a temperature of about 105° C to form said body, said bodybeing cokefied at a temperature above 800° C.